Just been looking into this myself (again!)
The Adams conversion can be done from a guy that flies from Stapleford (he also has modified it so that it will auto-off) and fits gels if you have the old fashioned foam seals.
As I need an extra headset I decided not to go for this but have tried out a variety of contenders at RD Aviation who are helpful and knowledgeable.
The Denalis (IIRC £320'sh) were a non starter as they seem incompatible with the DCs that I already have. My wife rated them best for wear together with the Bose X.
The Sennheiser 300 (£350)was fine but I thought not as comfortable as the DC 10-13X.(£525)
Most comfortable was the Bose X. This one is also the most expensive (at nearly £800)
IF I can find one or two good second hand DC 13.4's I will go for the conversion, failing that I will have to have a look in the kitty and decide which one it will be.
I did find it pays to have a look at some websites as there is quite a bit of variation in prices.
HTH and MHO as always.
No connection with any of the above individuals/companies mentioned.
FD